1. Field of the Invention
The present invention relates to motor controllers, and more specifically, to the sharing of signal and power pins on a motor controller.
2. Background Art
The direct current (DC) motor was one of the earliest machines used to convert electrical power into mechanical power. A permanent magnet (PM) converts electrical energy into mechanical energy through the interaction of two magnetic fields. One field is produced by a permanent magnet assembly and the other field is produced by an electrical current flowing in the motor windings. The two fields result in a torque that tends to rotate a rotor of the DC motor. As the rotor turns, the current in the windings is commutated to produce a continuous torque output. The permanent magnet (PM) motor is likely the most commonly used DC motor, but there are also other type of DC motors such as shunt that act in a similar fashion wherein the shunt wound field is permanently energized, and behaves like a permanent magnet.
In a permanent magnet motor, a coil of wire called the armature is arranged in the magnetic field of the magnet so that it rotates when a current is passed through it. A coil of wire moving in a magnetic field induces a voltage in the coil, and the current caused by applying a voltage to the coil therefore causes the armature to rotate and generate a voltage.
There is a back electromotive force (EMF) in the induced voltage caused by the armature""s movement that tends to cancel out the applied voltage so that the actual voltage across the armature is the difference between the applied voltage and the back EMF. The value of the back EMF is determined by factors such as the speed of rotation and the strength of the magnet. It should also be apparent that if you apply more voltage the motor will speed up, apply less and it will slow, which is the basic function of a speed controller does, which varies the voltage applied to the motor.
DC motors typically operate from a direct current (DC) power source, wherein the movement of the magnetic field is achieved by switching current between coils within the motor in a process called xe2x80x9ccommutationxe2x80x9d. Many DC motors are brush-type, and have built-in commutation, so that as the motor rotates, mechanical brushes automatically commutate coils on the rotor. There are various forms of motor speed control of DC motors in the prior art. One method to control the rotation speed of a DC motor is to control the motor driving voltage. For example, the higher the voltagexe2x80x94the higher the speed of the motor. In many applications a simple voltage regulation causes a significant power loss on the control circuit, requiring a pulse width modulation (PWM) scheme for more efficient DC motor control. The PWM technique operates by alternating the operating power to the motors, by turning the motor xe2x80x9conxe2x80x9d and xe2x80x9coffxe2x80x9d to modulate the current to the motor. It is the ratio of xe2x80x9conxe2x80x9d time to the xe2x80x9coffxe2x80x9d time that determines the speed of the motor. For certain applications it is necessary to change the direction of rotation for the motor. Normal permanent magnet motors change the rotation by changing the polarity of the operating power, such as switching from negative power supply to positive. The change in direction is typically implemented using a relay or an H bridge circuit.
A brushless DC motor relies on an external power drive to perform the commutation of stationary winding, generally copper, on the stator. The changing stator field causes the permanent magnet rotor to rotate. A brushless permanent magnet motor is the normally the optimal choice with respect to torque versus weight, but are also more expensive.
Electronically commutated brushless DC motor systems are used as drives for blowers and fans used in electronics, telecommunications and industrial equipment applications. There is a wide variety of different brushless motors for various applications. Some are designed to rotate at a constant speed, such as in disk drives, while others control the speed by varying the applied voltage, such as the motors used in fans. Some brushless DC motors even have a built-in tachometer that generates pulses as the motor rotates. In the commercial environment, users select brush type DC motors when low system cost is a priority, and use brushless motors to satisfy higher end requirements.
There are numerous high volume commercial applications for DC motors and motor controllers. For example, the market for cellular phone vibrating motor systems, used to provide a silent xe2x80x9cringingxe2x80x9d system is a 300 to 400 million units per year. In addition, the market for other simple motors is an additional 400 million/year. Therefore, even a small incremental cost saving is very significant.
It is reported by a major cell phone maker that this motor is one of the top failure mechanisms in cellular phones. These failures are caused by brush contact problems in brush type motors. These motors operate at a high speed, which is stressful on the brushes, making a brushless motor more attractive, though more costly.
There are many examples of pin sharing in the prior art. A concept of sharing a voltage supply and input pins is described in U.S. Pat. No. 3,735,378 relating to lighting systems and U.S. Pat. No. 5,247,239 discloses a voltage converter. U.S. Pat. No. 3,753,378 relates to a lamp failure indicating apparatus, wherein control signals generated from two detector networks detecting the operation of two lamp arrays are provided to an output amplifier through two diodes.
Pin sharing is also commercially available from companies such as National Semiconductor, Allegro Microsystems, and Melexis. Their datasheets generally show a method of sharing voltage supply with the output, in what is commonly called a two wire current loop. This configuration is well known in the art and illustrated in FIG. 1. The supply voltage 5 connects to the pin sharing circuit 10 and there is a current sensor 15 coupled to the supply line to sense the current into the device 10. A more common example of pin sharing it the common telephone that shares supply voltage with both input and output wires, with a switching system disposed between the phone company system and the residential phones.
Another example of pin sharing is described in U.S. Pat. No. 6,300,736 (""736), where there are no power supply pins. The power supply voltage for the Hall plate and Hall amplifier are taken from the xe2x80x9cOffxe2x80x9d output pin, through a switch. A complex digital controller synchronizes the Vdd switch and the gate drive of the power FETs to insure an uninterrupted Vdd. The block diagram of ""736 illustrates this complex approach to sharing, requiring two voltage regulators, complex switching and timing circuitry, high voltage (40V) transmission gates, etc. The higher complexity of ""736 is only a useful advantage in low voltage applications such as 2V or 3V, which are a very small portion of the total market for two phase brushless DC motors.
The Japanese Patent Application Laid-Open No. 4-317598 (""598) discloses a motor driving circuit and a fan driving circuit, wherein the fan driving circuit can be driven without providing a power supply by counter electromotive force generated in each coil while a motor is driven. The switching transistors are individually switched xe2x80x98Onxe2x80x99 and xe2x80x98Offxe2x80x99 to rotate, and current caused by counter electromotive force, which is generated in each coil, enters into a fan driving circuit transistor capable of operating as a regulator. Thus, each terminal of each of the switching transistor switchably connects to the fan driving circuit transistor. The ""598 patent does not disclose that the magnet sensor detects the rotor magnet, and that the regulator supplies power to the magnet sensor.
What is needed is a cost-effective and simplistic scheme for pin sharing. The pin sharing scheme should be flexible to allow incorporation in different designs. Such a scheme should also be practical for manufacturing concerns so as to be simple to incorporate into present manufactured designs. In addition, the pin sharing should reduce cost and complexity of manufactured designs.
The present invention has been made in consideration of the aforementioned background, and a general object is a device and method that reduces the cost of the motor controller chip. The present invention is an improved scheme for the sharing of pins between two or more functions. In this case voltage supply and output pins are shared, however other examples will be shown where voltage supply and inputs or outputs are shared as well. This invention focuses on a specific application with a simplified and improved method, saving significant cost that translates into other applications and fields that are appreciated by those skilled in the art.
A further object is a brushless motor combined with this novel proposed low cost and highly reliable circuit for sharing pins, thus eliminating a pin. The elimination of a pin offers a cost improvement and also a reliability improvement.
A preferred embodiment of the present invention utilizes simplified timing, where the switching simply follows the magnetic switching detected by the Hall sensor as the motor magnet passes. There are no added delays, and only very small propagation delays of the circuitry.
An object of the present invention is a controller using a diode instead of a switch, wherein a pair of power transistors is respectively connected to a voltage regulator through a diode and there are no switches. When the voltage of an output terminal of one of the power transistors is high, the power transistor is electrically connected to the voltage regulator. When the voltage of an output terminal of the other power transistor is low, it is not electrically connected to the voltage regulator. Accordingly, the two power transistors are electrically connectable to the voltage regulator. Even in a xe2x80x98highxe2x80x99 state where the voltages of the output terminals both become high as would momentarily appear during the full operation, the power transistors are switchably connected to the voltage regulator so the regulator can supply stabilized voltage to a magnetic sensor.
The present invention uses the inherent delays in the drive circuitry to avoid simultaneous conduction of both drivers. That is, when both drivers are switched (xe2x80x98Onxe2x80x99 to xe2x80x98Offxe2x80x99 and xe2x80x98Offxe2x80x99 to xe2x80x98Onxe2x80x99) the conducting driver will be xe2x80x98Offxe2x80x99 before the other conducts. Simultaneous conduction is undesirable in that it creates noise and wastes power by trying to turn the motor both clockwise (CW) and counter clockwise (CCW) at the same time. By designing the drivers to turn xe2x80x98Onxe2x80x99 slowly and turn xe2x80x98Offxe2x80x99 quickly, it can be seen that during the switching from one driver to the other, that both V1 and V2 will be high for a few microseconds, thereby eliminating the prior art problems. Slow xe2x80x98Onxe2x80x99 is accomplished by using an RC delay such that the gate drive ramps slowly. Fast xe2x80x98Offxe2x80x99 is obtained by discharging the gate capacitance with an N-CH transistor that bypasses the RC delay.
One object of the invention is a pin sharing controller for a DC motor, comprising a supply voltage with a magnetic sensor that generates a sensor output signal based upon an imposed magnetic field. There is a first transistor coupled to said sensor output for switchably coupling to the supply voltage through a first output pin, with a second transistor coupled to an inverted sensor output for switchably coupling to the supply voltage through a second output pin. A voltage regulator is coupled to a first diode and to the first output pin, and coupled to a second diode and the second output pin, wherein the voltage regulator provides an operating voltage for the magnetic sensor.
A further object includes the pin sharing controller, wherein the controller is a package having three pins. It also encompasses the magnetic sensor being a Hall plate and a Hall amplifier. There can also be an inverter coupled to the second transistor providing the inverted sensor output. The transistors can be field effect transistors. The diodes can be selected from the group comprising integrated diodes and discrete diodes.
An additional object is the pin sharing controller, wherein the first transistor switchably connects to the first output pin when the output signal is xe2x80x98Offxe2x80x99. In addition, wherein the second transistor switchably connects to the second output pin when the output signal is xe2x80x98Offxe2x80x99. Furthermore, wherein the first transistor and said second transistor are not connected to the respective first and second output pins simultaneously.
Yet a further object includes wherein the controller system comprises a resistor/capacitor (RC) delay so the first and second transistor are slowly switched. It also includes a transistor bypass of the RC delay.
An object of the invention is a pin sharing controller for a DC motor, comprising a supply voltage and a magnetic sensor that generates a sensor output signal based upon an imposed magnetic field. There is a first transistor coupled to the sensor output for switchably coupling to the supply voltage through a first output pin. A second transistor is coupled to an inverted sensor output for switchably coupling to the supply voltage through a second output pin. A voltage regulator is coupled to a first resistor and to the first output pin, and also coupled to a second resistor and the second output pin, wherein the voltage regulator provides an operating voltage for the magnetic sensor.
Yet a further object is a pin sharing controller for a DC motor, comprising a supply voltage with a magnetic sensor that generates a sensor output signal based upon an imposed magnetic field and having a first transistor coupled to the sensor output for switchably coupling to the supply voltage through a first output pin. There is a second transistor coupled to an inverted sensor output for switchably coupling to the supply voltage through a second output pin. A first voltage regulator is coupled to a first diode and to the first output pin, and a second voltage regulator is coupled to a second diode and to a second output pin.
Other objects, features and advantages are apparent from description in conjunction with the accompanying drawings.